Debonding and transfer techniques for hetero-epitaxially grown graphene, and products including the same

ABSTRACT

Certain example embodiments of this invention relate to the use of graphene as a transparent conductive coating (TCC). In certain example embodiments, graphene thin films grown on large areas hetero-epitaxially, e.g., on a catalyst thin film, from a hydrocarbon gas (such as, for example, C 2 H 2 , CH 4 , or the like). The graphene thin films of certain example embodiments may be doped or undoped. In certain example embodiments, graphene thin films, once formed, may be lifted off of their carrier substrates and transferred to receiving substrates, e.g., for inclusion in an intermediate or final product. Graphene grown, lifted, and transferred in this way may exhibit low sheet resistances (e.g., less than 150 ohms/square and lower when doped) and high transmission values (e.g., at least in the visible and infrared spectra).

FIELD OF THE INVENTION

Certain example embodiments of this invention relate to thin filmscomprising graphene. More particularly, certain example embodiments ofthis invention relate to the use of graphene as a transparent conductivecoating (TCC). In certain example embodiments, graphene thin films grownon large areas hetero-epitaxially, e.g., on a catalyst thin film, from ahydrocarbon gas (such as, for example, C₂H₂, CH₄, or the like). Thegraphene thin films of certain example embodiments may be doped orundoped. In certain example embodiments, graphene thin films, onceformed, may be lifted off of their carrier substrates and transferred toreceiving substrates, e.g., for inclusion in an intermediate or finalproduct.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

Indium tin oxide (ITO) and fluorine-doped tin oxide (FTO or SnO:F)coatings are widely used as window electrodes in opto-electronicdevices. These transparent conductive oxides (TCOs) have been immenselysuccessful in a variety of applications. Unfortunately, however, the useof ITO and FTO is becoming increasingly problematic for a number ofreasons. Such problems include, for example, the fact that there is alimited amount of the element indium available on Earth, the instabilityof the TCOs in the presence of an acide or base, their susceptibility toion diffusion from ion conducting layers, their limited transparency inthe near infrared region (e.g., power-rich spectrum), high leakagecurrent of FTO devices caused by FTO structure defects, etc. The brittlenature of ITO and its high deposition temperature can also limit itsapplications. In addition, surface asperities in SnO2:F may causeproblematic arcing.

Thus, it will be appreciated that there is a need in the art for smoothand patternable electrode materials with good stability, hightransparency, and excellent conductivity.

The search for novel electrode materials with good stability, hightransparency, and excellent conductivity is ongoing. One aspect of thissearch involves identifying viable alternatives to such conventionalTCOs. In this regard, the inventor of the instant invention hasdeveloped a viable transparent conductive coating (TCC) based on carbon,specifically graphene.

The term graphene generally refers to one or more atomic layers ofgraphite, e.g., with a single graphene layer or SGL being extendible upto n-layers of graphite (e.g., where n can be as high as about 10).Graphene's recent discovery and isolation (by cleaving crystallinegraphite) at the University of Manchester comes at a time when the trendin electronics is to reduce the dimensions of the circuit elements tothe nanometer scale. In this respect, graphene has unexpectedly led to anew world of unique opto-electronic properties, not encountered instandard electronic materials. This emerges from the linear dispersionrelation (E vs. k), which gives rise to charge carriers in graphenehaving a zero rest mass and behaving like relativistic particles. Therelativistic-like behavior delocalized electrons moving around carbonatoms results from their interaction with the periodic potential ofgraphene's honeycomb lattice gives rise to new quasi-particles that atlow energies (E<1.2 eV) are accurately described by the(2+1)-dimensional Dirac equation with an effective speed of lightν_(F)≈c/300=10⁶ ms⁻¹. Therefore, the well established techniques ofquantum electrodynamics (QED) (which deals with photons) can be broughtto bear in the study of graphene—with the further advantageous aspectbeing that such effects are amplified in graphene by a factor of 300.For example, the universal coupling constant α is nearly 2 in graphenecompared to 1/137 in vacuum. See K. S. Novoselov, “Electrical FieldEffect in Atomically Thin Carbon Films,” Science, vol. 306, pp. 666-69(2004), the contents of which are hereby incorporated herein.

Despite being only one-atom thick (at a minimum), graphene is chemicallyand thermally stable (although graphene may be surface-oxidized at 300degrees C.), thereby allowing successfully fabricated graphene-baseddevices to withstand ambient conditions. High quality graphene sheetswere first made by micro-mechanical cleavage of bulk graphite. The sametechnique is being fine-tuned to currently provide high-quality graphenecrystallites up to 100 μm² in size. This size is sufficient for mostresearch purposes in micro-electronics. Consequently, most techniquesdeveloped so far, mainly at universities, have focused more on themicroscopic sample, and device preparation and characterization ratherthan scaling up.

Unlike most of the current research trends, to realize the fullpotential of graphene as a possible TCC, large-area deposition of highquality material on substrates (e.g., glass or plastic substrates) isessential. To date, most large-scale graphene production processes relyon exfoliation of bulk graphite using wet-based chemicals and startswith highly ordered pyrolytic graphite (HOPG) and chemical exfoliation.As is known, HOPG is a highly ordered form of pyrolytic graphite with anangular spread of the c axes of less than 1 degree, and usually isproduced by stress annealing at 3300 K. HOPG behaves much like a puremetal in that it is generally reflective and electrically conductive,although brittle and flaky. Graphene produced in this manner is filteredand then adhered to a surface. However, there are drawbacks with theexfoliation process. For example, exfoliated graphene tends to fold andbecome crumpled, exists as small strips and relies on a collage/stitchprocess for deposition, lacks inherent control on the number of graphenelayers, etc. The material so produced is often contaminated byintercalates and, as such, has low grade electronic properties.

An in-depth analysis of the carbon phase diagram shows process windowconditions suitable to produce not only graphite and diamond, but alsoother allotropic forms such as, for example, carbon nano-tubes (CNT).Catalytic deposition of nano-tubes is done from a gas phase attemperatures as high as 1000 degrees C. by a variety of groups.

In contrast with these conventional research areas and conventionaltechniques, certain example embodiments of this invention relate to ascalable technique to hetero-epitaxially grow mono-crystalline graphite(n as large as about 15) and convert it to high electronic grade (HEG)graphene (n<about 3). Certain example embodiments also relate to the useof HEG graphene in transparent (in terms of both visible and infraredspectra), conductive ultra-thin graphene films, e.g., as an alternativeto the ubiquitously employed metal oxides window electrodes for avariety of applications (including, for example, solid-state solarcells). The growth technique of certain example embodiments is based ona catalytically driven hetero-epitaxial CVD process which takes place atemperature that is low enough to be glass-friendly. For example,thermodynamic as well as kinetics principles allow HEG graphene films tobe crystallized from the gas phase on a seed catalyst layer at atemperature less than about 700 degrees C.

Certain example embodiments also use atomic hydrogen, which has beenproven to be a potent radical for scavenging amorphous carbonaceouscontamination on substrates and being able to do so at low processtemperatures. It is also extremely good at removing oxides and otheroverlayers typically left by etching procedures.

Certain example embodiments of this invention relate to a method ofisolating a graphene thin film. The graphene thin film ishetero-epitaxially grown on a catalyst thin film. A polymer-basedcoating is disposed on the graphene thin film on a surface thereofopposite the catalyst thin film. The polymer-based coating is cured. Thegraphene thin film and the polymer-based coating is caused to bereleased from the catalyst thin film.

In certain example embodiments, the catalyst thin film is disposed on aback support substrate, with the back support substrate being formed onthe catalyst thin film on a surface thereof opposite the graphene thinfilm. A thin film release layer is disposed between the back supportsubstrate and the catalyst thin film.

In certain example embodiments, the graphene thin film and thepolymer-based coating is released from the catalyst thin film by etchingaway the catalyst thin film.

In certain example embodiments, the graphene thin film and thepolymer-based coating are disposed, directly or indirectly, on a targetreceiving substrate using contact pressure, with the graphene thin filmbeing closer to the target receiving substrate than the polymer-basedcoating. The polymer-based layer may be removed by dissolving it using asolvent and/or through exposure to UV radiation.

Certain example embodiments of this invention relate to a method ofdisposing a graphene thin film on a target receiving substrate. Thegraphene thin film is hetero-epitaxially grown on a catalyst thin film.A polymer-based coating is disposed on the graphene thin film on asurface thereof opposite the catalyst thin film. The graphene thin filmand the polymer-based coating are caused to be released from thecatalyst thin film. The graphene thin film and the polymer-based coatingare disposed, directly or indirectly, on the target receiving substrateusing contact pressure, with the graphene thin film being closer to thetarget receiving substrate than the polymer-based coating. Thepolymer-based layer is removed by exposing it to a solvent and/or UVradiation.

Certain example embodiments of this invention relate to a method ofdisposing a graphene thin film on a target receiving substrate. Thegraphene thin film is hetero-epitaxially grown on a metal catalyst thinfilm. The graphene thin film and the catalyst thin film are disposed,directly or indirectly, on the target receiving substrate. The catalystthin film below the graphene is electrochemically anodized so as torender the catalyst thin film a substantially transparent metal oxide.

Certain example embodiments of this invention relate to a method ofdisposing a graphene thin film on a target receiving substrate. Thegraphene thin film is hetero-epitaxially grown on a catalyst thin film.An adhesive is applied to the graphene thin film on a surface thereofopposite the catalyst thin film. The graphene thin film is caused to bereleased from the catalyst thin film. The graphene thin film is adheredto the target receiving substrate.

The features, aspects, advantages, and example embodiments describedherein may be combined to realize yet further embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages may be better and morecompletely understood by reference to the following detailed descriptionof exemplary illustrative embodiments in conjunction with the drawings,of which:

FIG. 1 is a high level flowchart illustrating the overall techniques ofcertain example embodiments;

FIG. 2 is an example schematic view of the catalytic growth techniquesof certain example embodiments, illustrating the introduction of thehydrocarbon gas, the carbon dissolving, and the possible results ofquenching, in accordance with certain example embodiments;

FIG. 3 is a flowchart illustrating a first example technique for dopinggraphene in accordance with certain example embodiments;

FIG. 4 is a flowchart illustrating a second example technique for dopinggraphene in accordance with certain example embodiments;

FIG. 5 is an example schematic view illustrating a third exampletechnique for doping graphene in accordance with certain exampleembodiments;

FIG. 6 is a graph plotting temperature vs. time involved in the dopingof graphene in accordance with certain example embodiments;

FIG. 7 is an example layer stack useful in the graphene release ordebonding techniques of certain example embodiments;

FIG. 8 is an example schematic view of a lamination apparatus that maybe used to dispose the graphene on the target glass substrate inaccordance with certain example embodiments;

FIG. 9 is a cross-sectional schematic view of a reactor suitable fordepositing high electronic grade (HEG) graphene in accordance with anexample embodiment;

FIG. 10 is an example process flow that illustrates certain of theexample catalytic CVD growth, lift-off, and transfer techniques ofcertain example embodiments;

FIG. 11 is an image of a sample graphene produced according to certainexample embodiments;

FIG. 12 is a cross-sectional schematic view of a solar photovoltaicdevice incorporating graphene-based layers according to certain exampleembodiments;

FIG. 13 is a cross-sectional schematic view of a touch screenincorporating graphene-based layers according to certain exampleembodiments; and

FIG. 14 is a flowchart illustrating an example technique for forming aconductive data/bus line in accordance with certain example embodiments;and

FIG. 15 is a schematic view of a technique for forming a conductivedata/bus line in accordance with certain example embodiments.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Certain example embodiments of this invention relate to a scalabletechnique to hetero-epitaxially grow mono-crystalline graphite (n aslarge as about 15) and convert it to high electronic grade (HEG)graphene (n<about 3). Certain example embodiments also relate to the useof HEG graphene in transparent (in terms of both visible and infraredspectra), conductive ultra-thin graphene films, e.g., as an alternativeto the more ubiquitously employed metal oxides window electrodes for avariety of applications (including, for example, solid-state solarcells). The growth technique of certain example embodiments is based ona catalytically driven hetero-epitaxial CVD process which takes place atemperature that is low enough to be glass-friendly. For example,thermodynamic as well as kinetics principles allow HEG graphene films tobe crystallized from the gas phase on a seed catalyst layer (e.g., at atemperature less than about 600 degrees C.).

FIG. 1 is a high level flowchart illustrating the overall techniques ofcertain example embodiments. As shown in FIG. 1, the overall techniquesof certain example embodiments can be classified as belonging to one offour basic steps: graphene crystallization on a suitable back support(step S101), graphene release or debonding from the back support (stepS103), graphene transference to the target substrate or surface (stepS105), and incorporation of the target substrate or surface into aproduct (step S107). As explained in greater detail below, it will beappreciated that the product referred to in step S107 may be anintermediate product or a final product.

Example Graphene Crystallization Techniques

The graphene crystallization techniques of certain example embodimentsmay be thought of as involving “cracking” a hydrocarbon gas andre-assembling the carbon atoms into the familiar honeycomb structureover a large area (e.g., an area of about 1 meter, or larger), e.g.,leveraging the surface catalytic pathway. The graphene crystallizationtechniques of certain example embodiments take place at high temperatureand moderate pressures. Illustrative details of this example processwill be described in detail below.

The catalytic growth techniques of certain example embodiments aresomewhat related to the techniques that have been used to grow graphiteover a hetero-epitaxial area. A catalyst for graphene crystallization isdisposed on a suitable back support. The back support may be anysuitable material capable of withstanding high heats (e.g., temperaturesup to about 1000 degrees C.) such as, for example, certain ceramics orglass products, zirconium inclusive materials, aluminum nitridematerials, silicon wafers, etc. A thin film is disposed, directly orindirectly, on the back support, thereby ensuring that its surface issubstantially uncontaminated prior to the crystallization process. Theinventor of the instant invention has discovered that graphenecrystallization is facilitated when the catalyst layer has asubstantially single-orientation crystal structure. In this regard,small grains have been determined to be less advantageous, since theirmosaic structure ultimately will be transferred to the graphene layer.In any event, the particular orientation of the crystal structure hasbeen found to be largely insignificant for graphene crystallization,provided that the catalyst layer, at least in substantial part, has asingle-orientation crystal structure. Indeed, the comparative absence of(or low) grain boundaries in the catalyst has been found to result inthe same or a similar orientation for the grown graphene, and has beenfound to provide for high electrical grade (HEG) graphene.

The catalyst layer itself may be disposed on the back support by anysuitable technique such as, for example, sputtering, combustion vapordeposition (CVD), flame pyrolysis, etc. The catalyst layer itself maycomprise any suitable metal or metal-inclusive material. For instance,the catalyst layer may comprise, for example, metals such as nickel,cobalt, iron, permalloy (e.g., nickel iron alloys, generally comprisingabout 20% iron and 80% nickel), alloys of nickel and chromium, copper,and combinations thereof. Of course, other metals may be used inconnection with certain example embodiments. The inventor has discoveredthat catalyst layers of or including nickel are particular advantageousfor graphene crystallization, and that alloys of nickel and chromium areyet more advantageous. Furthermore, the inventor has discovered that theamount of chromium in nickel-chromium layers (also sometimes callednichrome or NiCr layers) can be optimized so as to promote the formationof large crystals. In particular, 3-15% Cr in the NiCr layer ispreferable, 5-12% Cr in the NiCr layer is more preferable, and 7-10% ofCr in the NiCr layer is still more preferable. The presence of vanadiumin the metal thin film also has been found to be advantageous to promotelarge crystal growth. The catalyst layer may be relatively thin orthick. For example, the thin film may be 50-1000 nm thick, morepreferably 75-750 nm thick, and still more preferably 100-500 nm thick.A “large crystal growth” may in certain example instances includecrystals having a length along a major axis on the order of 10 s ofmicrons, and sometimes even larger.

Once the catalyst thin film is disposed on the back support, ahydrocarbon gas (e.g., C₂H₂ gas, CH₄ gas, etc.) is introduced in achamber in which the back support with the catalyst thin film disposedthereon is located. The hydrocarbon gas may be introduced at a pressureranging from about 5-150 mTorr, more preferably 10-100 mTorr. Ingeneral, the higher the pressure, the faster the growth of the graphene.The back support and/or the chamber as a whole is/are then heated todissolve or “crack open” the hydrocarbon gas. For example, the backsupport may be raised to a temperature in the range of 600-1200 degreesC., more preferably 700-1000 degrees C., and still more preferably800-900 degrees C. The heating may be accomplished by any suitabletechnique such as, for example, via a short wave infrared (IR) heater.The heating may take place in an environment comprising a gas such asargon, nitrogen, a mix of nitrogen and hydrogen, or other suitableenvironment. In other words, the heating of the hydrocarbon gas may takeplace in an environment comprising other gasses in certain exampleembodiments. In certain example embodiments, it may be desirable to usea pure hydrocarbon gas (for example, with C₂H₂), whereas it may bedesirable to use a mix of hydrocarbon gas an another inert or other gas(for example, CH₄ mixed with Ar).

The graphene will grow in this or another suitable environment. To stopthe growth and to help ensure that the graphene is grown on the surfaceof the catalyst (e.g., as opposed to being embedded within thecatalyst), certain example embodiments employ a quenching process. Thequenching may be performed using an inert gas such as, for example,argon, nitrogen, combinations thereof, etc. To promote graphene growthon the surface of the catalyst layer, the quenching should be performedfairly quickly. More particularly, it has been found that quenching toofast or too slow results in poor or no graphene growth on the surface ofthe catalyst layer. Generally, quenching so as to reduce the temperatureof the back support and/or substrate from about 900 degrees C. to 700degrees (or lower) over the course of several minutes has been found topromote good graphene growth, e.g., via chemisorption. In this regard,FIG. 2 is an example schematic view of the catalytic growth techniquesof certain example embodiments, illustrating the introduction of thehydrocarbon gas, the carbon dissolving, and the possible results ofquenching, in accordance with certain example embodiments.

The growth process of graphene imposes the strict film thicknessrelation t=n×SLG, where n involves some discrete number of steps.Identifying very rapidly if graphene has been produced and determiningthe value of n over the film area is roughly equivalent to measuringfilm quality and uniformity in one single measurement. Although graphenesheets can be seen by atomic force and scanning electron microscopy,these techniques are time consuming and can also lead to contaminationof the graphene. Therefore, certain example embodiments employ a phasecontrast technique that enhances the visibility of graphene on theintended catalyst surfaces. This may be done with a view to mapping anyvariation in n-value over the deposition surface on the metalliccatalyst film. The technique relies on the fact that the contrast ofgraphene may be enhanced substantially by spin coating a material ontoit. For example, a widely used UV curable resist (e.g., PMMA) may bespin coated, screen printed, gravure coated, or otherwise disposed onthe graphene/metal/back support, e.g., at a thickness sufficient to makethe film visible and continuous (e.g., around 1 micron thick). Asexplained in greater detail below, the inclusion of a polymer resistalso may facilitate the lift-off process of the graphene prior to itstransfer to the final surface. That is, in addition to providing anindication as to when graphene formation is complete, the polymer resistalso may provide a support for the highly elastic graphene when themetal layer is released or otherwise debonded from the back support asexplained in detail below.

In the event that a layer is grown too thick (either intentionally orunintentionally), the layer can be etched down, for example, usinghydrogen atoms (H*). This technique may be advantageous in a number ofexample situations. For instance, where growth occurs too quickly,unexpectedly, unevenly, etc., H* can be used to correct such problems.As another example, to ensure that enough graphene is grown, graphitemay be created, graphane may be deposited, and the graphane may beselectively etched back to the desired n-level HEG graphene, e.g., usingH*. As still another example, H* can be used to selectively etch awaygraphene, e.g., to create conductive areas and non-conductive areas.This may be accomplished by applying an appropriate mask, performing theetching, and then removing the mask, for example.

Theoretical studies of graphene has shown that the mobility of carrierscan be higher than 200,000 cm²/(V·s). Experimental measurements of gasphase treated hetero-epitaxial grown graphene show resistivity as low as3×10⁻⁶ Ω-cm, which is better than that of silver thin films. The sheetresistance for such graphene layers has been found to be about 150ohms/square. One factor that may vary is the number of layers ofgraphene that are needed to give the lowest resistivity and sheetresistance, and it will be appreciated that the desired thickness of thegraphene may vary depending on the target application. In general,graphene suitable for most applications may be n=1-15 graphene, morepreferably n=1-10 graphene, still more preferably n=1-5 graphene, andsometimes n=2-3 graphene. An n=1 graphene layer has been found to resultin a transmission drop of about 2.3-2.6%. This reduction in transmissionhas been found to be generally linear across substantially all spectra,e.g., ranging from ultraviolet (UV), through visible, and through IR.Furthermore, the loss in transmission has been found to be substantiallylinear with each successive incrementation of n.

Example Doping Techniques

Although a sheet resistance of 150 ohms/square may be suitable forcertain example applications, it will be appreciated that a furtherreduction in sheet resistance may be desirable for different exampleapplications. For example, it will be appreciated that a sheetresistance of 10-20 ohms/square may be desirable for certain exampleapplications. The inventor of the instant invention has determined thatsheet resistance can be lowered via the doping of the graphene.

In this regard, being only one atomic layer thick, graphene exhibitsballistic transport on a submicron scale and can be doped heavily—eitherby gate voltages or molecular adsorbates or intercalates in the casewhere n≧2—without significant loss of mobility. It has been determinedby the inventor of the instant invention that that in graphene, asidefrom the donor/acceptor distinction, there are in general two differentclasses of dopants, namely, paramagnetic and nonmagnetic. In contrast toordinary semiconductors, the latter type of impurities act generally asrather weak dopants, whereas the paramagnetic impurities cause strongdoping: Because of the linearly vanishing, electron-hole symmetricdensity of states (DOS) near the Dirac point of graphene, localizedimpurity states without spin polarization are pinned to the center ofthe pseudo-gap. Thus, impurity states in graphene distinguish stronglyfrom their counterparts in usual semiconductors, where the DOS in thevalence and conduction bands are very different and impurity levels liegenerally far away from the middle of the gap. Although one might notexpect a strong doping effect which requires existence of well-defineddonor (or acceptor) levels several tenths of electron volt away from theFermi level, if the impurity has a local magnetic moment, its energylevels split more or less symmetrically by the Hund exchange, of theorder of 1 eV, which provides a favorable situation for a strong dopingimpurity effects on the electronic structure of two-dimensional systemswith Dirac-like spectrum such as those present in graphene. This line ofreasoning may be used to guide the choice of molecules that form bothparamagnetic single molecules and diamagnetic dimers systems to dopegraphene and enhance its conductivity from 10³ S/cm to 10⁵ S/cm, andsometimes even to 10⁶ S/cm.

Example dopants suitable for use in connection with certain exampleembodiments include nitrogen, boron, phosphorous, fluorides, lithium,potassium, ammonium, etc. Sulfur-based dopants (e.g., sulfur dioxide)also may be used in connection with certain example embodiments. Forexample, sulfides present in glass substrates may be caused to seep outof the glass and thus dope the graphene-based layer. Several examplegraphene doping techniques are set forth in greater detail below.

FIG. 3 is a flowchart illustrating a first example technique for dopinggraphene in accordance with certain example embodiments. The FIG. 3example technique essentially involves ion beam implanting the dopingmaterial in the graphene. In this example technique, graphene is grownon a metal catalyst (step S301), e.g., as described above. The catalystwith the graphene formed thereon is exposed to a gas comprising amaterial to be used as the dopant (also sometimes referred to as adopant gas) (step S303). A plasma is then excited within a chambercontaining the catalyst with the graphene formed thereon and the dopantgas (S305). An ion beam is then used to implant the dopant into thegraphene (S307). Example ion beam techniques suitable for this sort ofdoping are disclosed in, for example, U.S. Pat. Nos. 6,602,371;6,808,606; and Re. 38,358, and U.S. Publication No. 2008/0199702, eachof which is hereby incorporated herein by reference. The ion beam powermay be about 10-200 ev, more preferably 20-50 ev, still more preferably20-40 ev.

FIG. 4 is a flowchart illustrating a second example technique for dopinggraphene in accordance with certain example embodiments. The FIG. 4example technique essentially involves pre-implanting solid statedopants in the target receiving substrate, and then causing those solidstate dopants to migrate into the graphene when the graphene is appliedto the receiving substrate. In this example technique, graphene is grownon a metal catalyst (step S401), e.g., as described above. The receivingsubstrate is pre-fabricated so as to include solid-state dopants therein(step S403). For example, the solid-state dopants may be included viathe melting in the formulation in the glass. About 1-10 atomic %, morepreferably 1-5 atomic %, and still more preferably 2-3 atomic % dopantmay be included in the glass melt. The graphene is applied to thereceiving substrate, e.g., using one of the example techniques describedin detail below (step S405). Then, the solid-state dopants in thereceiving substrate are caused to migrate into the graphene. The heatused in the deposition of the graphene will cause the dopants to migratetowards the graphene layer being formed. Similarly, additionally dopedfilms can be included on the glass and the dopants therein can be causedto migrate through these layers by thermal diffusion, for example,creating a doped graphene (n>=2) layer.

An ion beam also can be used to implant the dopants directly in theglass in certain example embodiments. The ion beam power may be about10-1000 ev, more preferably 20-500 ev, still more preferably 20-100 ev.When an intermediate layer is doped and used to provide impurities forthe graphene, the ion beam may operate at about 10-200 ev, morepreferably 20-50 ev, still more preferably 20-40 ev.

FIG. 5 is an example schematic view illustrating a third exampletechnique for doping graphene in accordance with certain exampleembodiments. The FIG. 5 example techniques essentially involvespre-implanting solid state dopants 507 in the metal catalyst layer 503,and then causing those solid state dopants 507 to migrate through thecatalyst layer 503 as the graphene is being formed, thereby creating adoped graphene 509 on the surface of the catalyst layer 503. Moreparticularly, in this example technique, the catalyst layer 503 isdisposed on the back support 505. The catalyst layer 503 includessolid-state dopants 507 therein. In other words, the catalyst hassolid-state dopant atoms inside its bulk (e.g., from about 1-10%, morepreferably about 1-5%, and most preferably about 1-3%). Hydrocarbon gas501 is introduced proximate to the catalyst layer 503 formed, at a hightemperature. The solid-state dopants 507 in the catalyst layer 503 arecaused to migrate towards the outer surface thereof, e.g., by this hightemperature, as the graphene crystallization takes place. The rate atwhich the dopants arrive at the surface has been found to be a functionof the catalyst thickness and temperature. The crystallization isstopped via quenching and, ultimately, a doped graphene 509 is formed onthe surface of the catalyst layer 503′. Following the formation of thedoped graphene 509, the catalyst layer 503′ now has fewer (or no)solid-state dopants 507 located therein. One advantage of this exampletechnique relates to the potential to control the ultrathin film growthby judiciously varying the metal surface temperature, partial pressure,and residence time of the deposition gas species, as well as thereactive radicals used in quenching rate process.

It will be appreciated that these example doping techniques may be usedalone and/or in various combinations and sub-combinations with oneanother and/or further techniques. It also will be appreciated thatcertain example embodiments may include a single dopant material ormultiple dopant materials, e.g., by using a particular example techniqueonce, a particular technique repeatedly, or through a combination ofmultiple techniques one or more times each. For example, p-type andn-type dopants are possible in certain example embodiments.

FIG. 6 is a graph plotting temperature vs. time involved in the dopingof graphene in accordance with certain example embodiments. As indicatedabove, the cooling may be accomplished using, for example, an inert gas.In general, and also as indicated above, the high temperature may beabout 900 degrees C. in certain example embodiments, and the lowtemperature may be about 700 degrees C., and the cooling may take placeover several minutes. The same heating/cooling profile as that shown inFIG. 6 may be used regardless of whether the graphene is doped.

Example Graphene Release/Debonding and Transfer Techniques

Once graphene has been hetero-epitaxially grown, it may be released ordebonded from the metal catalyst and/or the back support, e.g., prior tobeing placed on substrate to be incorporated into the intermediate orfinal product. Various procedures may be implemented for liftingepitaxial films from their growth substrates in accordance with certainexample embodiments. FIG. 7 is an example layer stack useful in thegraphene release or debonding techniques of certain example embodiments.Referred to FIG. 7, in certain example embodiments, an optional releaselayer 701 may be provided between the back support 505 and the catalystlayer 503. This release layer 701 may be of or include, for example,zinc oxide (e.g., ZnO or other suitable stoichiometry). Post-graphenedeposition, the graphene 509/metal catalyst layer 503/release layer 701stack coated substrate 505 may receive a thick overcoat (e.g., severalmicrons thick) layer of polymer 703, e.g., applied via spin coating,dispensed by a meniscus flow, etc., which may be cured. As alluded toabove, this polymer layer 703 may act as a backbone or support for thegraphene 509 during lift-off and/or debonding, keeping the extremelyflexible graphene film continuous, while also reducing the likelihood ofthe graphene film curling up, creasing, or otherwise deforming.

Also as alluded to above, PMMA may be used as the polymer that allowsthe graphene to become visible by phase contrast and for support priorto and/or during lift-off. However, a broad range of polymers whosemechanical and chemical properties can be matched to those of graphenemay be used during the support phase, as well as the release transferphase in connection with certain example embodiments. The work forlift-off may be performed in parallel with the main epitaxial growthbranch, e.g., by experimenting with graphene films that can bechemically exfoliated from graphite.

The release layer may be chemically induced to de-bond thegraphene/metal from mother substrate once the polymer layer disposedthereon. For example, in the case of a zinc oxide release layer, washingin vinegar may trigger the release of the graphene. The use of a zincoxide release layer also is advantageous, inasmuch as the inventor ofthe instant invention has discovered that the metal catalyst layer alsois removed from the graphene with the release layer. It is believed thatthis is a result of the texturing caused by the zinc oxide release layertogether with its inter-linkages formed with the grains in the catalystlayer. It will be appreciated that this reduces (and sometimes eveneliminates) the need to later remove the catalyst layer.

Certain lift-off/debonding and transfer techniques essentially regardthe original substrate as a reusable epitaxial growth substrate. Assuch, a selective etching to undercut and dissolve away the metalliccatalyst thin film away from the epitaxially grown (with polymer on top)graphene may be desirable in such example embodiments. Thus, thecatalyst layer may be etched off, regardless of whether a release layeris used, in certain example embodiments. Suitable etchants include, forexample, acids such as hydrochloric acid, phosphoric acid, etc.

The final recipient glass substrate surface may be prepared so as toreceive the graphene layer. For example, a Langmuir Blodgett film (e.g.,from a Langmuir-Blodgett acid) may be applied to the glass substrate.The final recipient substrate alternatively or additionally may becoated with a smooth graphenophillic layer such as, for example, asilicone-based polymer, etc., making the latter receptive to thegraphene. This may help to ensure electrostatic bonding, thuspreferentially allowing the transfer of the graphene during transfer.The target substrate may additionally or alternatively be exposed to UVradiation, e.g., to increase the surface energy of the target substrateand thus make it more receptive to the graphene.

The graphene may be applied to the substrate via blanket stamping and/orrolling in certain example embodiments. Such processes allow thegraphene previously grown and chemisorbed onto the metal carrier to betransferred onto the recipient glass by contact pressure. As oneexample, the graphene may be applied to the substrate via one or morelamination rollers, e.g., as shown in FIG. 8. In this regard, FIG. 8shows upper and lower rollers 803 a and 803 b, which will apply pressureand cause the graphene 509 and polymer layer 703 to be laminated to thetarget substrate 801. As noted above, the target substrate 801 have asilicon-inclusive or other graphenophillic layer disposed thereon tofacilitate the lamination. It will be appreciated that the polymer layer703 will be applied as the outermost layer and that the graphene 509will be closer to (or even directly on) the target substrate 801. Incertain example embodiments, one or more layers may be provided on thesubstrate prior to the application of the graphene.

Once the graphene is disposed on the target substrate, the polymer layermay be removed. In certain example embodiments, the polymer may bedissolved using an appropriate solvent. When a photosensitive materialsuch as PMMA is used, it may be removed via UV light exposure. Ofcourse, other removal techniques also are possible.

It will be appreciated that the catalyst thin film may be etched offafter the graphene has been applied to the target substrate in certainexample embodiments, e.g., using one of the example etchants describedabove. The choice of etchant also may be based on the presence orabsence of any layers underlying the graphene.

Certain example embodiments more directly electrochemically anodize themetal catalyst thin film below the graphene. In such exampleembodiments, the graphene itself may act as the cathode, as the metalbelow is anodized into a transparent oxide while still being bonded tothe original substrate. Such example embodiments may be used to bypassthe use of the polymer overcoat by essentially performing the lift-offand transfer processes in one step. However, anodization byelectrochemical means may affect the electronic properties of thegraphene and thus may need to be compensated for. In certain exampleembodiments, the catalyst layer below the graphene may be oxidized inother ways to make it transparent. For example, a conductive oxide maybe used to “link” the graphene-based layer to a substrate,semiconductor, or other layer. In this regard, cobalt, chrome cobalt,nickel chrome cobalt, and/or the like may be oxidized. In certainexample embodiments, this may also reduce the need for graphenelift-off, making the transfer, manipulation, and other handling ofgraphene easier.

The graphene also may be picked up using an adhesive or tape-likematerial in certain example embodiments. The adhesive may be positionedon the target substrate. The graphene may be transferred to the targetsubstrate, e.g., following the application of pressure, by more stronglyadhering to the substrate than to the tape, etc.

Example Reactor Design

Showerhead reactors typically employ a perforated or porous planarsurface to dispense reactant gasses more-or-less uniformly over a secondparallel planar heated surface. Such a configuration may be used to growgraphene using the example hetero-epitaxial techniques described herein.Showerhead reactors also are advantageous for the processing of largesquare ultra-smooth glass or ceramic substrate. A basic schematic of ashowerhead reactor is FIG. 9, with the plenum design being enlarged. Inother words, FIG. 9 is a cross-sectional schematic view of a reactorsuitable for depositing high electronic grade (HEG) graphene inaccordance with an example embodiment. The reactor includes a bodyportion 901 with several inlets and outlets. More particularly, a gasinlet 903 is provided at the top and in the approximate horizontalcenter of the body portion 901 of the reactor. The gas inlet 903 mayreceive gas from one or more sources and thus may provide various gassesincluding, for example, the hydrocarbon gas, the gas(ses) used to formthe environment during hetero-epitaxial growth, the quenching gas(ses),etc. The flow and flux of the gas will be described in greater detailbelow, e.g., with reference to the plenum design of the showerhead 907.A plurality of exhaust ports 905 may be provided at the bottom of thebody portion 901 of the reactor. In the FIG. 9 example embodiment, twoexhaust ports 905 are provided proximate to the extremes of the bodyportion 901 of the reactor, e.g., so as to draw out gas provided by thegas inlet 903 that generally will flow through substantially theentirety of the body portion 901. It will be appreciated that more orfewer exhaust ports 905 may be provided in certain example embodiments(e.g., further exhaust ports 905 may be provided in the approximatehorizontal center of the body portion 901 of the reactor, at the top orsides of the body portion 901 of the reactor, etc.).

The back support substrate 909 may be cleaned and have the catalyst thinfilm disposed thereon (e.g., by physical vapor deposition or PVD,sputtering, CVD, flame pyrolysis, or the like) prior to entry into thereactor by a load-lock mechanism in certain example embodiments. Interms of susceptor design, the surface of the back support substrate 909may be rapidly heated (e.g., using an RTA heater, a shortwave IR heater,or other suitable heater that is capable of inductively heating thesubstrate and/or layers thereon without necessarily also heating theentire chamber) to a controllable temperature level and uniformity thatallows (i) the metal film to crystallize and activate, and (ii) thepreferential deposition of graphene of substantially uniform andcontrollable thickness from a gas phase precursor on its surface. Theheater may be controllable so as to account for the parameter depositionrate/(temperature*thickness) of catalyst ratio. The back supportsubstrate 909 may move through the reactor in the direction R or may sitstationary under the showerhead 907. The showerhead 907 may be cooled,e.g., using a cooling fluid or gas introduced by one or more coolantinlets/outlets 913. In brief, and as shown in the FIG. 9 enlargement,the plenum design may include a plurality of apertures in the bottom ofthe showerhead 907, with each such aperture being only a few millimeterswide.

Changing the ceiling gap Hc, or the height between the bottom surface ofthe showerhead 907 and the top surface upon which the back supportsubstrate 909 moves, may have several effects. For example, the chambervolume and thus the surface-to-volume ratio may be modified, therebyaffecting the gas residence time, consumption time, and radialvelocities. Changes in the residence time have been found to stronglyinfluence the extent of gas phase reactions. A showerhead configurationoperated as shown in FIG. 9 (with a hot surface below a cooled surface)has the potential for Benard variety natural convection if operated athigh pressures (e.g., in the hundreds of Torr), and such a tendency isstrongly influenced by the height through the Rayleigh number (adimensionless number associated with buoyancy driven flow, also known asfree convection or natural convection; when it exceeds a critical valuefor a fluid, heat transfer is primarily in the form of convection).Accordingly, the ceiling gap Hc may be varied through simple hardwarechanges, by providing adjustable mounting of the substrate electrode,etc., so as to affect the hetero-epitaxial growth of the graphene.

The FIG. 9 example embodiment is not necessarily intended to operate aplasma within the reactor. This is because the crystalline film growthmechanism is by hetero-epitaxy by surface sorption (generally occurringonly on the catalyst). Growth from the plasma phase has been found togive rise to mostly amorphous films and also has been found to allow theformation of macro-particle or dust formation that can greatly reducefilm quality and result in pinholes that would be detrimental for aone-to-ten atomic layer film. Instead, certain example embodiments mayinvolve making graphite (e.g., monocrystalline graphite), etching it tographane (e.g., of a certain n-value), and turning the graphane intographene (e.g., into HEG graphene). Of course, an in-situ end-pointtechnique may be implemented as a feed-back parameter.

In certain example embodiments, an ion beam source may be locatedin-line but external to the reactor of FIG. 9, e.g., to perform dopingin accordance with the example techniques described above. However, incertain example embodiments, an ion beam source may be located withinthe body portion of a reactor.

Example Process Flow

FIG. 10 is an example process flow that illustrates certain of theexample catalytic CVD growth, lift-off, and transfer techniques ofcertain example embodiments. The example process shown in FIG. 10 beginsas the back support glass is inspected, e.g., using a conventional glassinspection method (step S1002) and washed (step S1004). The back supportglass may then be cleaned using ion beam cleaning, plasma ashing, or thelike (step S1006). The catalyst (e.g., a metal catalyst) is disposed onthe back support, e.g., using PVD (step S1008). It is noted that thecleaning process of step S1006 may be accomplished within the graphenecoater/reactor in certain example embodiments of this invention. Inother words, the back support glass with or without the metal catalystthin film formed thereon may be loaded into the graphene coater/reactorprior to step S1006 in certain example embodiments, e.g., depending onwhether the metal catalyst layer is deposited within or prior to thecoater/reactor. The catalytic deposition of an n-layer graphene may thentake place (step S1010). The graphene may be etched down by introducinghydrogen atoms (H*) in certain example embodiments, and the grapheneoptionally may be doped, e.g., depending on the target application (stepS1012). The end of the graphene formation is detected, e.g., bydetermining whether enough graphene has been deposited and/or whetherthe H* etching has been sufficient (step S1014). To stop the grapheneformation, a rapid quenching process is used, and the back support glasswith the graphene formed therein exits the reactor/coater (step S1016).Visual inspection optionally may be performed at this point.

Following graphene formation, a polymer useful in the transference ofthe graphene may be disposed on the graphene, e.g., by spin, blade, orother coating technique (step S1018). This product optionally may beinspected, e.g., to determine whether the requisite color change takesplace. If it has, the polymer may be cured (e.g., using heat, UVradiation, etc.) (step S1020), and then inspected again. The metalcatalyst may be under-etched or otherwise released (step S1022), e.g.,to prepare the graphene for lift-off (step S1024).

Once lift-off has been achieved, the polymer and the graphene optionallymay be inspected and then washed, e.g., to remove any remainingunder-etchants and/or non-cured polymer (step S1026). Another optionalinspection process may be performed at this point. A surfactant may beapplied (step S1028), pins are placed at least into the polymer (stepS1030), and the membrane is flipped (step S1032), e.g., with the aid ofthese pins. The lift-off process is now complete, and the graphene isnow ready to be transferred to the recipient substrate.

The recipient substrate is prepared (step S1034), e.g., in a clean room.The surface of the recipient substrate may be functionalized, e.g., byexposing it to a UV light to increase its surface energy, to applygraphenophillic coatings thereto, etc. (step S1036). Thegraphene/polymer membrane may then be transferred onto the hostsubstrate (step S1038).

Once the transfer is complete, the receiving substrate with the grapheneand polymer attached thereto may be fed into a module to remove thepolymer (step S1040). This may be done by exposing the polymer to UVlight, heat, chemicals, etc. The substrate with the graphene and atleast partially dissolved polymer may then be washed (step S1042), withany excess water or other materials evaporated and dried off (stepS1044). This polymer removal process may be repeated, as necessary.

Following the removal of the polymer, the sheet resistance of thegraphene on the substrate may be measured (step S1046), e.g., using astandard four-point probe. Optical transmission (e.g., Tvis, etc.) alsomay be measured (step S1048). Assuming that the intermediate or finalproducts meet quality standards, they may be packaged (step S1050).

Using these techniques, sample films were prepared. The sample filmsexhibited high conductivity of 15500 S/cm and transparency of more than80% over the 500-3000 nm wavelength. Furthermore, the films showed goodchemical and thermal stability. FIG. 11 is an image of a sample grapheneproduced according to certain example embodiments. The FIG. 11 imagehighlights the lift-off of the hetero-epitaxially grown graphene from apermalloy thin film.

Example Graphene-Inclusive Applications

As alluded to above, graphene-based layers may be used in a wide varietyof applications and/or electronic devices. In such example applicationsand/or electronic devices, ITO and/or other conductive layers simply maybe replaced by graphene-based layers. Making devices with graphene willtypically involve making contacts with metals, degenerate semiconductorslike ITO, solar cell semiconductors such as a-Si and CdTe among others,and/or the like.

Despite having a zero band-gap and a vanishing density of states (DOS)at the K-points in the Brillouin zone, free standing graphene exhibitsmetallic behavior. However, adsorption on metallic, semiconducting orinsulating substrate can alter its electronic properties. To compensatefor this, additionally, or in the alternative, in example applicationsand/or electronic devices, the graphene-based layer may be doped inaccordance with any semiconductor layers adjacent thereto. That is, incertain example embodiments, if a graphene-based layer is adjacent to ann-type semiconductor layer, the graphene-based layer may be doped withan n-type dopant. Likewise, in certain example embodiments, if agraphene-based layer is adjacent to a p-type semiconductor layer, thegraphene-based layer may be doped with a p-type dopant. Of course, theshift in Fermi level in graphene with respect to the conical points maybe modeled, e.g., using density functional theory (DFT). Band-gapcalculations show that metal/graphene interfaces can be classified intotwo broad classes, namely, chemisorption and physisorption. In thelatter case, a shift upward (downward) means that electron (holes) aredonated by the metal to the graphene. Thus, it is possible to predictwhich metal or TCO to use to as contacts to the graphene depending onthe application.

A first example electronic device that may make use of one or moregraphene-based layers is a solar photovoltaic device. Such exampledevices may include front electrodes or back electrodes. In suchdevices, the graphene-based layers may simply replace the ITO typicallyused therein. Photovoltaic devices are disclosed in, for example, U.S.Pat. Nos. 6,784,361, 6,288,325, 6,613,603 and 6,123,824; U.S.Publication Nos. 2008/0169021; 2009/0032098; 2008/0308147; and2009/0020157; and application Ser. Nos. 12/285,374, 12/285,890, and12/457,006, the disclosures of which are hereby incorporated herein byreference.

Alternatively, or in addition, doped graphene-based layers may beincluded therein so as to match with adjacent semiconductor layers. Forinstance, FIG. 12 is a cross-sectional schematic view of a solarphotovoltaic device incorporating graphene-based layers according tocertain example embodiments. In the FIG. 12 example embodiment, a glasssubstrate 1202 is provided. For example and without limitation, theglass substrate 1202 may be of any of the glasses described in any ofU.S. patent application Ser. Nos. 11/049,292 and/or 11/122,218, thedisclosures of which are hereby incorporated herein by reference. Theglass substrate optionally may be nano-textured, e.g., to increase theefficiency of the solar cell. An anti-reflective (AR) coating 1204 maybe provided on an exterior surface of the glass substrate 1202, e.g., toincrease transmission. The anti-reflective coating 1204 may be asingle-layer anti-reflective (SLAR) coating (e.g., a silicon oxideanti-reflective coating) or a multi-layer anti-reflective (MLAR)coating. Such AR coatings may be provided using any suitable technique.

One or more absorbing layers 1206 may be provided on the glass substrate1202 opposite the AR coating 1204, e.g., in the case of a back electrodedevice such as that shown in the FIG. 12 example embodiment. Theabsorbing layers 1206 may be sandwiched between first and secondsemi-conductors. In the FIG. 12 example embodiment, absorbing layers1206 are sandwiched between n-type semiconductor layer 1208 (closer tothe glass substrate 1202) and p-type semiconductor 1210 (farther fromthe glass substrate 1202). A back contact 1212 (e.g., of aluminum orother suitable material) also may be provided. Rather than providing ITOor other conductive material(s) between the semiconductor 1208 and theglass substrate 1202 and/or between the semiconductor 1210 and the backcontact 1212, first and second graphene-based layers 1214 and 1216 maybe provided. The graphene-based layers 1214 and 1216 may be doped so asto match the adjacent semiconductor layers 1208 and 1210, respectively.Thus, in the FIG. 12 example embodiment, graphene-based layer 1214 maybe doped with n-type dopants and graphene-based layer 1216 may be dopedwith p-type dopants.

Because it is difficult to directly texture graphene, an optional layer1218 may be provided between the glass substrate 1202 and the firstgraphene-based layer 1214. However, because graphene is very flexible,it generally will conform to the surface on which it is placed.Accordingly, it is possible to texture the optional layer 1218 so thatthe texture of that layer may be “transferred” or otherwise reflected inthe generally conformal graphene-based layer 1214. In this regard, theoptional textured layer 1218 may comprise zinc-doped tin oxide (ZTO). Itis noted that one or both of semiconductors 1208 and 1210 may bereplaced with polymeric conductive materials in certain exampleembodiments.

Because graphene is essentially transparent in the near and mid-IRranges implies that the most penetrating long wavelength radiation maypenetrate and generate carriers deep into the i-layer of both single andtandem junction solar cells. This implies that the need to texture backcontacts may not be needed with graphene-based layers, as the efficiencywill already be increased by as much as several percentage points.

Screen-printing, evaporation, and sintering technologies and CdCl2treatment at high temperatures are currently used in CdS/CdTe solar cellheterojunctions. These cells have high fill factors (FF>0.8). However,series resistance Rs is an efficiency limiting artifact. In Rs, there isa distributed part from sheet resistance of the CdS layer and a discretecomponent associated with the CdTe and graphite based contact on top ofit. The use of one or more graphene-based layers may help reduce bothcontributions to Rs, while preserving good heterojunction properties. Byincluding graphene in such a solar structure for both front and backcontact arrangements, a substantial efficiency boost may be achieved.

It will be appreciated that certain example embodiments may involvesingle junction solar cells, whereas certain example embodiments mayinvolve tandem solar cells. Certain example embodiments may be CdS,CdTe, CIS/CIGS, a-Si, and/or other types of solar cells.

Another example embodiment that may incorporate one or moregraphene-based layers is a touch panel display. For instance, the touchpanel display may be a capacitive or resistive touch panel displayincluding ITO or other conductive layers. See, for example, U.S. Pat.Nos. 7,436,393; 7,372,510; 7,215,331; 6,204,897; 6,177,918; and5,650,597, and application Ser. No. 12/292,406, the disclosures of whichare hereby incorporated herein by reference. The ITO and/or otherconductive layers may be replaced in such touch panels may be replacedwith graphene-based layers. For example, FIG. 13 is a cross-sectionalschematic view of a touch screen incorporating graphene-based layersaccording to certain example embodiments. FIG. 13 includes an underlyingdisplay 1302, which may, in certain example embodiments, be an LCD,plasma, or other flat panel display. An optically clear adhesive 1304couples the display 1302 to a thin glass sheet 1306. A deformable PETfoil 1308 is provided as the top-most layer in the FIG. 13 exampleembodiment. The PET foil 1308 is spaced apart from the upper surface ofthe thin glass substrate 1306 by virtual of a plurality of pillarspacers 1310 and edge seals 1312. First and second graphene-based layers1314 and 1316 may be provided on the surface of the PET foil 1308 closerto the display 1302 and to the thin glass substrate 1306 on the surfacefacing the PET foil 1308, respectively. One or both graphene-basedlayers 1314 and 1316 may be patterned, e.g., by ion beam and/or laseretching. It is noted that the graphene-based layer on the PET foil maybe transferred from its growth location to the intermediate productusing the PET foil itself. In other words, the PET foil may be usedinstead of a photoresist or other material when lifting off the grapheneand/or moving it.

A sheet resistance of less than about 500 ohms/square for thegraphene-based layers is acceptable in embodiments similar to thoseshown in FIG. 13, and a sheet resistance of less than about 300ohms/square is advantageous for the graphene-based layers.

It will be appreciated that the ITO typically found in display 1302 maybe replaced with one or more graphene-based layers. For example, whendisplay 1302 is an LCD display, graphene-based layers may be provided asa common electrode on the color filter substrate and/or as patternedelectrodes on the so-called TFT substrate. Of course, graphene-basedlayers, doped or undoped, also may be used in connection with the designand fabrication of the individual TFTs. Similar arrangements also may beprovided in connection with plasma and/or other plat panel displays.

Graphene-based layers also may be used to create conductive data/buslines, bus bars, antennas, and/or the like. Such structures may beformed on/applied to glass substrates, silicon wafers, etc. FIG. 14 is aflowchart illustrating an example technique for forming a conductivedata/bus line in accordance with certain example embodiments. In stepS1401, a graphene-based layer is formed on an appropriate substrate. Inan optional step, step S1403, a protective layer may be provided overthe graphene-based layer. In step S1405, the graphene-based layer isselectively removed or patterned. This removal or patterning may beaccomplished by laser etching. In such cases, the need for a protectivelayer may be reduced, provided that the resolution of the laser is fineenough. Alternatively or in addition, etching may be performed viaexposure to an ion beam/plasma treatment. Also, as explained above, H*may be used, e.g., in connection with a hot filament. When an ionbeam/plasma treatment is used for etching, a protective layer may bedesirable. For example, a photoresist material may be used to protectthe graphene areas of interest. Such a photoresist may be applied, e.g.,by spin coating or the like in step S1403. In such cases, in anotheroptional step, S1407, the optional protective layer is removed. Exposureto UV radiation may be used with appropriate photoresists, for example.In one or more steps not shown, the conductive graphene-based patternmay be transferred to an intermediate or final product if it was notalready formed thereon, e.g., using any appropriate technique (such as,for example, those described above).

Although certain example embodiments have been described as etching awayor removing graphene-based layers, certain example embodiments maysimply change the conductivity of the graphene-based layer. In suchcases, some or all of the graphene may not be removed. However, becausethe conductivity has been suitably altered, only the appropriatelypatterned areas may be conductive.

FIG. 15 is a schematic view of a technique for forming a conductivedata/bus line in accordance with certain example embodiments. As shownin FIG. 15, the conductivity of the graphene is selectively changed byvirtue of exposure to an ion beam. A photoresist is applied in asuitable pattern, e.g., so as to protect desired portions of thegraphene-based layer, whereas the other portions of the graphene-basedlayer remain exposed to the ion beam/plasma.

Mobility data is shown in the table below after various samples havebeen deposited and etched.

Etched Thickness Rho Conductivty Mobility μ Samples Passes (Å) (Ωcm)(1/Ωcm) (cm{circumflex over ( )}2/Vs) A 25 8 1.03E−04 970000 120,000 B20 6 5.24E−03 1010000 143000 C 10 6 5.94E−02 1600000 150000 D 5 61.48E−02 1500000 160000

It will be appreciated that patterning the graphene in this and/or otherways may be advantageous for a number of reasons. For example, the layerwill be largely transparent. Thus, it is possible to provide “seamless”antennas where the pattern cannot be seen. A similar result may beprovided in connection with bus bars that may be incorporated intovehicle windows (e.g., for defrosting, antenna usage, poweringcomponents, etc.), flat panel (e.g., LCD, plasma, and/or other) displaydevices, skylights, refrigerator/freezer doors/windows, etc. This mayalso advantageously reduce the need for black frits often found in suchproducts. Additionally, graphene-based layers may be used in place ofITO in electrochromic devices.

Although certain example applications/devices have been describedherein, as shown above, it is possible to use graphene-based conductivelayers in place of or in addition to other transparent conductivecoatings (TCCs), such as ITO, zinc oxide, etc.

As used herein, the terms “on,” “supported by,” and the like should notbe interpreted to mean that two elements are directly adjacent to oneanother unless explicitly stated. In other words, a first layer may besaid to be “on” or “supported by” a second layer, even if there are oneor more layers therebetween.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A method of isolating a graphene thin film, the method comprising:hetero-epitaxially growing the graphene thin film on a catalyst thinfilm; disposing a polymer-based coating on the graphene thin film on asurface thereof opposite the catalyst thin film; curing thepolymer-based coating; and causing the graphene thin film and thepolymer-based coating to be released from the catalyst thin film.
 2. Themethod of claim 1, wherein the catalyst thin film is disposed on a backsupport substrate, the back support substrate being formed on thecatalyst thin film on a surface thereof opposite the graphene thin film,and wherein a thin film release layer is disposed between the backsupport substrate and the catalyst thin film.
 3. The method of claim ofclaim 2, wherein the release layer comprises zinc oxide.
 4. The methodof claim 2, wherein the graphene thin film and the polymer-based coatingis released from at least the substrate by chemically inducing therelease layer.
 5. The method of claim 3, wherein the graphene thin filmand the polymer-based coating is released from the substrate and thecatalyst thin film by chemically inducing the release layer usingvinegar.
 6. The method of claim 1, wherein the graphene thin film andthe polymer-based coating is released from the catalyst thin film byetching away the catalyst thin film.
 7. The method of claim 4, whereinthe graphene thin film and the polymer-based coating is released fromthe catalyst thin film by etching away at least a portion of thecatalyst thin film.
 8. The method of claim 1, further comprisingpreparing a target receiving substrate by coating the target receivingsubstrate with a graphenophillic coating.
 9. The method of claim 8,wherein the graphenophillic coating is a silicon inclusive coating or aLangmuir Blodgett film.
 10. The method of claim 1, further comprisingexposing a target receiving substrate to UV radiation to increase thetarget receiving substrate's surface energy, thereby making the targetreceiving substrate more receptive to the graphene thin film than itotherwise would be.
 11. The method of claim 1, further comprisingdisposing the graphene thin film and the polymer-based coating, directlyor indirectly, on a target receiving substrate using contact pressure,the graphene thin film being closer to the target receiving substratethan the polymer-based coating.
 12. The method of claim 11, wherein thedisposing of the graphene thin film and the polymer-based coating on thetarget receiving substrate is performed using blanket stamping.
 13. Themethod of claim 11, wherein the disposing of the graphene thin film andthe polymer-based coating on the target receiving substrate is performedusing one or more rollers.
 14. The method of claim 11, furthercomprising removing the polymer-based layer by dissolving it using asolvent and/or through exposure to UV radiation.
 15. A method ofdisposing a graphene thin film on a target receiving substrate, themethod comprising: hetero-epitaxially growing the graphene thin film ona catalyst thin film; disposing a polymer-based coating on the graphenethin film on a surface thereof opposite the catalyst thin film; causingthe graphene thin film and the polymer-based coating to be released fromthe catalyst thin film; disposing the graphene thin film and thepolymer-based coating, directly or indirectly, on the target receivingsubstrate using contact pressure, the graphene thin film being closer tothe target receiving substrate than the polymer-based coating; andremoving the polymer-based layer by exposing it to a solvent and/or UVradiation.
 16. The method of claim 15, wherein the polymer-based layeris PMMA.
 17. A method of disposing a graphene thin film on a targetreceiving substrate, the method comprising: hetero-epitaxially growingthe graphene thin film on a metal catalyst thin film; disposing thegraphene thin film and the catalyst thin film, directly or indirectly,on the target receiving substrate; and electrochemically anodizing thecatalyst thin film below the graphene so as to render the catalyst thinfilm a substantially transparent metal oxide.
 18. The method of claim18, wherein during the electrochemical anodizing, the graphene thin filmis caused to act as a cathode as the metal catalyst thin film isanodized.
 19. A method of disposing a graphene thin film on a targetreceiving substrate, the method comprising: hetero-epitaxially growingthe graphene thin film on a catalyst thin film; applying an adhesive tothe graphene thin film on a surface thereof opposite the catalyst thinfilm; causing the graphene thin film to be released from the catalystthin film; and adhering the graphene thin film to the target receivingsubstrate.
 20. The method of claim 19, wherein the graphene thin film isreleased from the catalyst thin film by virtue of a stronger bondbetween the graphene thin film and the adhesive than between thegraphene thin film and the catalyst thin film during peeling of theadhesive.
 21. The method of claim 19, wherein the graphene thin film isreleased from the catalyst thin film by selectively etching away thecatalyst thin film.